Symmetry of Neutron-InducedU235Fission at Individual Resonances. III

The symmetry of neutron-induced fission in ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ has been measured at a large number of epithermal levels with a time-of-flight energy-resolved beam from an underground nuclear explosion. The energy resolution was improved over previous similar "wheel" experiments. The symmetry of fission, as measured radiochemically by the ratio of ${}_{}{}^{115}{}_{}{}^{}\mathrm{Cd}$ to ${}_{}{}^{99}{}_{}{}^{}\mathrm{Mo}$, shows a bimodal distribution. If the results are averaged separately for the two apparent groups, the first group (I) has an average ${}_{}{}^{115}{}_{}{}^{}\mathrm{Cd}$/${}_{}{}^{99}{}_{}{}^{}\mathrm{Mo}$ ratio which is 0.593 times the thermal value; the second-group (II) average is 1.11 times the thermal value. The average fission width in I is one-half the average fission width in II. The numbers of levels assigned to I and II are 24 and 14, respectively. The energies of levels assigned to I are 19.30, 21.07, 22.94, 23.63, 26.44, 27.81, 30.91, 32.10, 33.55, 34.85, 40.51, 41.91, 43.41, 44.04, 45.79, 46.93, 48.06, 48.82, 51.37, 56.58, 57.83, 58.15, 60.25, and 61.10 eV; assignments to II are at 24.23, 25.65, 28.35, 34.39, 35.21, 35.75, 36.64, 38.42, 39.44, 44.75, 49.51, 52.27, 53.56, and 58.68 eV. From analogy with conclusions based on a similar set of observations in the fission of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ and on arguments derived from fission-channel theory, it is hypothesized that $J=4\mathrm{}$ in I and 3 in II.